The present invention relates to non-inflammable filaments, such as textile filaments, formed of two polymers, eeach containing acrylonitrile units and vinylidene chloride units. These filaments have a high chlorine content and exhibit low thermoplasticity.
Fibers based upon acrylonitrile polymers are in wide-spread use, particularly in the textile field, because of their excellent physical properties. However, these fibers have the distinct disadvantage that they ignite rather easily.
Synthetic fibers based upon chlorinated monomers, or predominantly based upon chlorinated monomers, are also known to the art, generally under the name "chlorofibers". Such fibers may contain up to 70% chlorine or so in practice. The chlorofibers are flame resistant but exhibit thermoplastic properties. That is, the fibers have a low sticking temperature and also exhibit high shrinkage at elevated temperatures, such as upon exposure to boiling water or steam. Because of the thermoplastic nature of these fibers, they have little use in textile applications.
The Wieckowski U.S. Pat. No. 3,288,888, issued Nov. 29, 1966, discloses the production of flame resistant acrylonitrile-vinylidene chloride polymer blend filaments by blending two different polymer components. One of the components is a polymer which contains acrylonitrile units but no vinylidene chloride units. Comonomers such as acrylic acid and methacrylic acid are used in amounts of up to 30%. The other polymeric component of the blend is a copolymer of acrylonitrile and vinylidene chloride, containing 30 to 70% vinylidene chloride. The two polymer components may be used in ratios of 2 to 98 parts of either component. The polymer components are completely compatible with one another, so that the resulting mixture can be spun into textile filaments. Because of this, the chlorine content of the polymer mixture generally is at a level of between 5 and 10%. However, such low chlorine contents are not high enough to impart the desired non-inflammable characteristics to the fibers. In this regard, the accepted criteria of non-inflammability of textile fibers is becoming stricter and stricter, and it is now generally recognized that the chlorine content of the fibers should be at least 25%, preferably at least 29%, by weight.
French Pat. No. 1,393,117 (corresponding to the above Wieckowski U.S. Pat. No. is slightly broader in proportions therein, indicating that the acrylonitrilevinylidene copolymer can contain less than 80% of vinylidene chloride and at least 20% acrylonitrile. The broadest disclosure of chlorine content in this French patent is about 4 to 20%.
French Pat. No., 1,211,700 is directed to spinable compositions of a mixture of polymers. One polymer, used in the amount of 95-70%, contains more than 80% of acrylonitrile units and less than 20% of a comonomer, while the second, halogenated polymer, used in an amount of 5-30%, contains more than 80% of vinyl chloride and/or vinylidene chloride units and less than 20% of a comonomer therewith. Polymers of this patent have a chlorine content of about 5 to 20%. However, the properties of fibers made from the polymer mixture of this patent are below the desired levels.